Flutter / Dart: StatefulWidget - access class variable inside Widget - flutter

Question

I declare a class variable for a StatefulWidget - in the code below it's someString.
Is it possible to use this variable in the build(…)-method without declaring it as static?
class MyClass extends StatefulWidget {
String someString;
MyClass() {
this.someString = "foo";
}
#override
_MyClassState createState() => _MyClassState();
}
class _MyClassState extends State<MyClass> {
_MyClassState();
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("someString - how to access it here?!"),
// title: Text(someString), is not possible, obviously
),
);
}
}
Thanks in advance for help!

Answer 1

Attention: MyClass should be immutable.
1. If someString will never change
Keep it inside MyClass but define it as final.
class MyClass extends StatefulWidget {
final String someString;
const MyClass({Key key, this.someString = 'foo'}) : super(key: key);
#override
_MyClassState createState() => _MyClassState();
}
Then, inside the State, you can use it as widget.someString:
class _MyClassState extends State<MyClass> {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('${widget.someString} is accessed here?!')),
);
}
}
2. If someString will change
It should be defined in the state.
class MyClass extends StatefulWidget {
final String initialValue;
const MyClass({Key key, this.initialValue = 'foo'}) : super(key: key);
#override
_MyClassState createState() => _MyClassState();
}
class _MyClassState extends State<MyClass> {
String someString;
#override
void initState() {
someString = widget.initialValue;
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('$someString is accessed here?!')),
body: Center(
child: OutlinedButton(
onPressed: () => setState(() => someString = 'NEW Value'),
child: Text('Update value'),
),
),
);
}
}